Soft capsules are used in a wide range of fields including pharmaceuticals, foods, and cosmetics. The most popular shell base for the soft capsules is gelatin, and gelatin is inexpensive and non-toxic and exhibits an excellent mechanical strength, shell-forming ability, and the like.
On the other hand, because of a recent problem of bovine spongiform encephalopathy (BSE) or for religious reasons, an alternative to animal-derived gelatin has been required, and capsules are no exception.
In view of the foregoing, a variety of investigations have been made on a capsule shell using a plant-derived base, and there have been previously reported, for example, a capsule shell including processed starch obtained by subjecting waxy corn starch to acid treatment and iota carrageenan (Patent Literature 1), a film-forming composition for a soft capsule including acid-decomposed waxy corn starch, a gelling agent, and a plasticizer (Patent Literature 2), a soft capsule outer shell formed by blending starch, A-carrageenan, a metal salt, dextrin, a plasticizer, and water (Patent Literature 3), and a soft capsule outer shell formed by blending a starch derivative mixture, a starch decomposed matter, a gum mix, reduced maltose, a plasticizer, and water (Patent Literature 4).